Marking menus are gesture-based menu selection techniques in which menu items are arranged radially and a user draws a stroke towards a desired item in order to select that item. Marking menus offer several features including selection strokes that are fast and easy to draw and an efficient novice to expert transition. However, a drawback of marking menus is that selection accuracy depends on the number of items that appear in the menu, referred to as “breadth.” Accuracy can decrease substantially for marking menus of breadth greater than eight items (referred to as breadth-8).
Hierarchical marking menus increase the total number of menu items available by allowing users to select from multiple submenus using a compound zigzag stroke or other designated stroke. For users to maintain a reasonable accuracy rate of greater than ninety percent, a breadth-8 menu can have a depth of at most two levels, thereby providing access to sixty-four unique items. While a breadth-12 menu generally cannot maintain acceptable accuracy beyond depth-1, a breadth-4 menu can maintain good accuracy up to depth-4.
Breaking compound selection strokes into a sequence of inflection-free strokes has been proposed. Such multi-stroke marking menus can allow users to work with breadth-8 menus up to depth-3 (resulting in 512 unique items), at an accuracy rate of ninety three percent. These multi-stroke marking menus can also improve selection speed and accuracy while providing better space efficiency than compound-stroke marking menus.
Although increasing menu depth increases the total number of menu items available, these deep hierarchies suffer from several challenges. For example, deeper items take longer to access because the user must draw more complex strokes to select the desired item. While increasing breadth would generate shallower hierarchies, to maintain acceptable accuracy rates, both compound-stroke and multi-stroke marking menus are limited to breadth-8.
The limitation on menu breadth can also force an unnatural conceptual grouping of menu items. For example, consider a painting application that allows users to select brush colors from a palette of sixteen choices. Since marking menus are generally limited to breadth-8, the painting application uses a two level marking menu for color selection. The menu designer therefore must unnaturally divide the sixteen colors into many different groups. The breadth-depth tradeoff for general menu hierarchies has concluded that in most cases breadth is preferable to depth.
Therefore, to overcome the aforementioned challenges, there is a need for variants of multi-stroke marking menus that are designed to increase menu breadth while maintaining efficiency and ease of selection.